The Accuracy of Initial U.S. Heart Transplant Candidate Rankings

Clinical Outcomes for Heart-Alone and Multiorgan Transplant Under the New Heart Allocation Policy Era

BACKGROUND

In October 2018, a new heart transplant allocation policy was implemented in the United States to address inequalities. Under the new policy, some patient outcomes for patients with heart transplant have improved; however, outcomes of multiorgan transplants combined with heart remain unclear.

METHODS

We examined the waitlist mortality, time to transplant, and posttransplant survival for all patients listed between 2013 and 2022 for multiorgan transplants with heart (n=3798) and compared the old policy era to the new policy era using cumulative incident curves and multivariable Cox regression models. Cumulative incidence curves also compared multiorgan transplants to patients listed for heart alone (n=31 840) under the new policy era.

RESULTS

Patients awaiting multiorgan transplants had higher use of intra-aortic balloon pumps (4.7% versus 11%) and extracorporeal membrane oxygenation support (2.4% versus 4.9%) in the new policy era. Under the new policy, despite receiving transplants sooner (n=2200 transplants, hazard ratio [HR], 1.74 [95% CI, 1.59-1.91]), patients who received multiorgan transplants had no change in waitlist mortality (n=340 deaths, HR, 1.06 [95% CI, 0.84-1.34]) compared with the old policy era. The rate of death post-multiorgan transplant was significantly higher in incidence curves under the new policy compared with the old policy era (log-rank P=0.02). However, in multivariable Cox models, the risk of death post-multiorgan transplant was similar under the new policy (n=287 deaths, HR, 1.11 [95% CI, 0.87-1.41]) compared with the old policy era.

CONCLUSIONS

Under the new policy, waitlist deaths have decreased for patients awaiting heart alone, but not for those awaiting multiorgan transplants. Post-transplant survival remains lower for patients who underwent multiorgan transplant (compared with heart-alone transplant), with no change under the new policy.

National Organ Procurement and Transplant Network Heart Allocation Policy: 6 Years Later

In 2014, the Organ Procurement and Transplant Network began reappraisal of the United States heart transplant allocation policy. Driven by ongoing discordance between organ supply and demand, high waitlist mortality, and increasing exception requests, the Thoracic Committee radically redesigned the priority scheme and drafted a 6-tiered algorithm, included durable device complications into policy, expanded broader sharing, and increased the number of mandatory listing variables to develop a future heart allocation score. This became the 2018 New Heart Allocation Policy. Changes in allocation priority have resulted in a significant increase in the use of temporary mechanical circulatory support in waitlisted candidates with a concomitant decrease in the number of patients bridged to transplanted with durable left ventricular assist device support. The number of exception requests continues to increase, particularly for patients listed status 2 and for multiorgan transplants. Importantly, fewer patients are being delisted for clinical improvement, suggesting missed opportunities for recovery. The current review will critically evaluate the 2018 heart allocation policy 6 years later, briefly focusing on the history of heart allocation in the United States, the current and evolving algorithms for candidate prioritization including continuous distribution, the impact of technology and innovation on transplant rates and future policy development, and the ongoing regulatory oversight and governance changes in the Organ Procurement and Transplant Network.

The Colorado Heart Failure Acuity Risk Model: A Mortality Model for Waitlisted Cardiac Transplant Patients

Background

Currently, there is no mathematical model used nationally to determine the medical urgency of patients on the heart transplant waitlist in the United States. While the current organ distribution system accounts for many patient factors, a truly objective model is needed to more reliably stratify patients by their medical acuity.

Objectives

The aim of the study was to develop risk scores (Colorado Heart failure Acuity Risk Model [CHARM] score) to predict mortality in adults waitlisted for heart transplant.

Methods

Risk scores were based on multivariable logistic regression models with mortality endpoints at 90 days, 180 days, 1 year, and 2 years. The models included serology data and patient history variables from waitlisted patients (N = 4,176) within the Scientific Registry of Transplant Recipients database from January 1, 2017, to September 2, 2023.

Results

The CHARM score included serum markers (brain natriuretic peptide, creatinine, sodium, aspartate aminotransferase, albumin, total bilirubin) and clinical variables (history of cardiac surgery, prior transplant, willingness to accept an hepatitis C virus positive heart, use of extracorporeal membrane oxygenation, use of mechanical life support, implantation of a cardiac defibrillator, and ventilator support prior to transplant). Sample holdout-validation for the models yielded average area under the curves of 0.825 (90-day), 0.805 (180-day), 0.779 (1-year), and 0.766 (2-year). Risk indices for all models were 99% correlated with observed mortality rates.

Conclusions

The CHARM score provides reliable calibration and prediction, offering an objective system for identifying critically ill patients on the heart transplant waitlist. The CHARM score will be useful in the era of continuous distribution to standardize organ allocation.

Impact of Heart Transplant Allocation Change on Waitlist Mortality and Posttransplant Mortality in Patients With Left Ventricular Assist Devices

BACKGROUND

In October 2018, the US heart transplant (HT) allocation system was revised giving patients with left ventricular assist device (LVAD) intermediate priority status. Few studies have examined the impact of this policy change on outcomes among patients with LVAD. We sought to determine how the allocation change impacted waitlist and posttransplant mortality in patients with LVAD.

METHODS

We retrospectively assessed the United Network for Organ Sharing registry for patients with LVAD who were listed for or underwent HT between October 2016 and October 2021. We evaluated waitlist mortality using competing risks analysis and a multivariable Fine-Gray model, and posttransplant mortality using Kaplan-Meier survival analysis and a multivariate proportional hazards model.

RESULTS

We analyzed data from 3835 patients with LVAD listed for HT and 3486 patients with LVAD who underwent HT during the study period. Listing for HT preallocation change was significantly associated with an increased risk of waitlist mortality (Gray P=0.0058) compared with postallocation change. After adjustment for covariates, mortality differences by listing era were attenuated, but LVAD brand was significantly associated with waitlist mortality (HM3 versus HMII; hazard ratio, 0.38 [95% CI, 0.21-0.69]; P=0.002; HVAD versus HMII; hazard ratio, 0.79 [95% CI, 0.48-1.30]; P=0.36; overall P=0.004). In contrast, HT postallocation change was associated with increased posttransplant mortality (log-rank P=0.0172) compared with preallocation change. In a multivariable analysis, the association with posttransplant mortality between transplant eras was attenuated, but ischemic time (hazard ratio, 1.16 [95% CI, 1.07-1.26]; P<0.001) and status at time of HT (Status 1-3 versus 4; hazard ratio, 1.29 [95% CI, 1.04-1.61]; P=0.02) were significantly associated with posttransplant mortality.

CONCLUSIONS

Among patients with LVAD, lower waitlist mortality postallocation change was likely driven by improved LVAD technology. Higher posttransplant mortality following the allocation change was largely attributable to longer ischemic times and patient acuity.

Development and Validation of a Risk Score Predicting Death Without Transplant in Adult Heart Transplant Candidates

Importance

The US heart allocation system prioritizes medically urgent candidates with a high risk of dying without transplant. The current therapy-based 6-status system is susceptible to manipulation and has limited rank ordering ability.

Objective

To develop and validate a candidate risk score that incorporates current clinical, laboratory, and hemodynamic data.

Design, Setting, and Participants

A registry-based observational study of adult heart transplant candidates (aged ≥18 years) from the US heart allocation system listed between January 1, 2019, and December 31, 2022, split by center into training (70%) and test (30%) datasets. Adult candidates were listed between January 1, 2019, and December 31, 2022.

Main Outcomes and Measures

A US candidate risk score (US-CRS) model was developed by adding a predefined set of predictors to the current French Candidate Risk Score (French-CRS) model. Sensitivity analyses were performed, which included intra-aortic balloon pumps (IABP) and percutaneous ventricular assist devices (VAD) in the definition of short-term mechanical circulatory support (MCS) for the US-CRS. Performance of the US-CRS model, French-CRS model, and 6-status model in the test dataset was evaluated by time-dependent area under the receiver operating characteristic curve (AUC) for death without transplant within 6 weeks and overall survival concordance (c-index) with integrated AUC.

Results

A total of 16 905 adult heart transplant candidates were listed (mean [SD] age, 53 [13] years; 73% male; 58% White); 796 patients (4.7%) died without a transplant. The final US-CRS contained time-varying short-term MCS (ventricular assist-extracorporeal membrane oxygenation or temporary surgical VAD), the log of bilirubin, estimated glomerular filtration rate, the log of B-type natriuretic peptide, albumin, sodium, and durable left ventricular assist device. In the test dataset, the AUC for death within 6 weeks of listing for the US-CRS model was 0.79 (95% CI, 0.75-0.83), for the French-CRS model was 0.72 (95% CI, 0.67-0.76), and 6-status model was 0.68 (95% CI, 0.62-0.73). Overall c-index for the US-CRS model was 0.76 (95% CI, 0.73-0.80), for the French-CRS model was 0.69 (95% CI, 0.65-0.73), and 6-status model was 0.67 (95% CI, 0.63-0.71). Classifying IABP and percutaneous VAD as short-term MCS reduced the effect size by 54%.

Conclusions and Relevance

In this registry-based study of US heart transplant candidates, a continuous multivariable allocation score outperformed the 6-status system in rank ordering heart transplant candidates by medical urgency and may be useful for the medical urgency component of heart allocation.